CN114388793A - Negative electrode for nonaqueous electrolyte secondary battery and nonaqueous electrolyte secondary battery comprising same - Google Patents
Negative electrode for nonaqueous electrolyte secondary battery and nonaqueous electrolyte secondary battery comprising same Download PDFInfo
- Publication number
- CN114388793A CN114388793A CN202111161779.1A CN202111161779A CN114388793A CN 114388793 A CN114388793 A CN 114388793A CN 202111161779 A CN202111161779 A CN 202111161779A CN 114388793 A CN114388793 A CN 114388793A
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- CN
- China
- Prior art keywords
- negative electrode
- secondary battery
- nonaqueous electrolyte
- electrolyte secondary
- active material
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/60—Selection of substances as active materials, active masses, active liquids of organic compounds
- H01M4/602—Polymers
- H01M4/604—Polymers containing aliphatic main chain polymers
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/027—Negative electrodes
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- H—ELECTRICITY
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Abstract
The purpose of the present invention is to provide a negative electrode for a nonaqueous electrolyte secondary battery, which has excellent durability. In order to solve the above problems, a negative electrode for a nonaqueous electrolyte secondary battery has a multi-branched molecule bonded to the particle surface of a negative electrode active material. By disposing the multi-branched polymer on the surface of the negative electrode active material, direct contact between the electrolyte and the lithium insertion surface of the negative electrode active material is suppressed, and therefore, decomposition of the electrolyte and growth of SEI can be suppressed. This reduces lithium consumption and improves long-term storage characteristics, and therefore, a nonaqueous electrolyte secondary battery with an improved capacity retention rate can be provided.
Description
Technical Field
The present invention relates to a negative electrode for a nonaqueous electrolyte secondary battery and a nonaqueous electrolyte secondary battery including the same.
Background
In recent years, with the spread of nonaqueous electrolyte secondary batteries, further improvement in performance has been expected. Therefore, various techniques have been developed to improve the performance of nonaqueous electrolyte secondary batteries.
In a lithium ion secondary battery as a nonaqueous electrolyte secondary battery, the following problems are known: when the solvent is decomposed on the surface of the negative electrode particle, a Solid Electrolyte interface film (SEI) grows, and working lithium is consumed, and thus, durability (capacity retention rate) is reduced. Therefore, various measures have been studied to improve the durability. Patent document 1 discloses the following method: the electrolyte additive is used to control the formation and composition of the SEI coating film, etc., to improve durability.
[ Prior Art document ]
(patent document)
Patent document 1: japanese patent laid-open publication No. 2019-192439
Disclosure of Invention
[ problems to be solved by the invention ]
However, if the concentration of the electrolyte additive is increased for higher durability, the conductivity of the electrolyte is lowered, and the battery output, low temperature characteristics, and the like are lowered. Further, there are also problems as follows: gas is generated in the SEI film formation stage, and defoaming and SEI formation reactions are repeated in stages, thereby consuming time and reducing production efficiency. Further, the durability is improved by stabilizing SEI by increasing the kinds of additives, but there are problems as follows: if the additive is added, a coating film can be formed, while the resistance increases and the output decreases.
The invention provides a negative electrode for a nonaqueous electrolyte secondary battery having excellent durability and a nonaqueous electrolyte secondary battery having the same. In the present technology, specific organic molecules are bound to the surface of the negative electrode, thereby designing an interface in the material, forming an organic artificial SEI. In particular, when a multi-branched molecule is bonded, desolvation can be promoted, and decomposition of the electrolytic solution is suppressed, so that the storage stability of the electrolytic solution is improved.
[ means for solving problems ]
(1) The present invention provides a negative electrode for a nonaqueous electrolyte secondary battery, which is characterized in that a multi-branched molecule is bonded to the surface of a negative electrode material comprising a negative electrode active material, a conductive assistant and a current collector.
According to the invention of (1), the multi-branched polymer is disposed, whereby direct contact between the electrolytic solution and the lithium insertion surface of the negative electrode active material is suppressed, and therefore, the electrolytic solution can be suppressed from being decomposed to cause SEI growth. Thus, lithium consumption is reduced, and long-term storage characteristics are improved, and therefore, a negative electrode for a nonaqueous electrolyte secondary battery having an improved capacity retention rate can be provided.
(2) The negative electrode for a nonaqueous electrolyte secondary battery according to the item (1), wherein the multi-branched molecule is composed of at least one compound selected from the group consisting of a dendron, a dendrimer and a hyperbranched polymer.
According to the invention of (2), the multi-branched dendrimer is bonded to the outside of the particles of the negative electrode active material to form the organic artificial SEI, whereby the lithium intercalation surface can be covered with the dendrimer. This suppresses direct contact between the electrolyte and the lithium intercalation surface, and therefore prevents decomposition of the electrolyte and SEI growth, thereby improving the durability of the electrode and the electrolyte.
(3) The negative electrode for a nonaqueous electrolyte secondary battery according to (1) or (2), wherein the multi-branched molecule has a number average molecular weight of 300 or more and has 4 or more molecular terminal portions in one molecule.
According to the invention (3), the lithium intercalation surface on the surface of the negative electrode active material particle can be sufficiently covered, and direct contact between the electrolyte and the lithium intercalation surface is suppressed, so that the durability of the electrode and the electrolyte can be improved.
(4) The negative electrode for a nonaqueous electrolyte secondary battery according to any one of (1) to (3), wherein the negative electrode active material has a functional group on a surface thereof, and the multi-branched molecule is bonded to the functional group.
According to the invention (4), since the dendrimer can be immobilized on the surface of the negative electrode active material, a more stable organic artificial SEI can be formed, and durability can be improved.
(5) The negative electrode for a nonaqueous electrolyte secondary battery according to any one of (1) to (4), wherein a filling rate of the negative electrode active material in the negative electrode is 65% or more.
According to the invention (5), since the SEI component can be controlled, not only durability but also output and charging performance of the battery can be improved. Therefore, even if the density of the negative electrode is increased, the reaction resistance at the active material interface can be suppressed, and the resistance can be prevented from increasing. Thus, a negative electrode for a nonaqueous electrolyte secondary battery having a high energy density can be provided.
(6) Further, the present invention provides a nonaqueous electrolyte secondary battery comprising the negative electrode for nonaqueous electrolyte secondary batteries according to any one of (1) to (5).
According to the invention of (6), a nonaqueous electrolyte secondary battery having improved durability of the electrode and the electrolyte solution can be provided.
(7) The nonaqueous electrolyte secondary battery according to the item (6), wherein at least one compound selected from the group consisting of vinylene carbonate, fluoroethylene carbonate and propane sultone is further added to the electrolyte.
According to the invention of (7), the electrolytic solution to which the compound having reductive decomposition property and being liable to form the SEI film is added is used in the battery of (6), whereby the added compound is decomposed in preference to the electrolytic solution to form the SEI film of the negative electrode, and therefore the durability of the electrolytic solution is further improved. By using the electrode of (1) to (5) in combination, the SEI can be stabilized, the types of additives can be reduced, and the resistance of the electrolyte can be reduced.
Drawings
Fig. 1 is a schematic sectional view showing a negative electrode in the present embodiment.
Fig. 2 is a graph showing the relationship between the depth and the composition in example 3.
Fig. 3 is a graph showing the relationship between the depth and the composition in comparative example 1.
Detailed Description
An embodiment of the present invention will be described below with reference to the drawings. The contents of the present invention are not limited to the description of the following embodiments.
< lithium ion secondary battery >
The lithium ion secondary battery 100 of the present embodiment includes: a positive electrode including a positive electrode mixture layer formed on a positive electrode collector; a negative electrode 1 including a negative electrode mixture layer 12 formed on a negative electrode current collector; a separator that electrically insulates the positive electrode from the negative electrode 1; an electrolyte; and a container (not shown) that accommodates the positive electrode, the negative electrode 1, the separator, and the electrolyte.
In the container, the positive electrode mixture layer and the negative electrode mixture layer are opposed to each other with the separator interposed therebetween, and the electrolyte is stored below the positive electrode mixture layer and the negative electrode mixture layer. The end of the separator is immersed in the electrolyte.
(electrode mixture layer)
The positive electrode mixture layer is composed of a positive electrode active material, a conductive additive and a binder. The negative electrode mixture layer 12 is composed of a negative electrode active material 11, a conductive auxiliary agent, and a binder (binder). The particles of numerous bipolar active materials are aggregated and arranged in the bipolar mixture layer.
[ active Material ]
As the positive electrode active material, for example, lithium composite oxide (LiNi) can be usedXCoyMnzO2(x+y+z＝1)、LiNiXCoyA1zO2(x + y + z ═ 1)), lithium iron phosphate (LiFePO)4(LFP)), etc. One of these may be used, or two or more of them may be used in combination.
Examples of the negative electrode active material 11 include carbon powder (amorphous carbon) and silicon dioxide (SiO)x) Titanium composite oxide (Li)4Ti5O7、TiO2、Nb2TiO7)、One or two or more of tin composite oxide, lithium alloy, metallic lithium, and the like can be used. As the carbon powder, one or more of soft carbon (graphitizable carbon), hard carbon (graphitizable carbon), and graphite (graphite) can be used.
[ conductive auxiliary agent ]
Examples of the conductive aid used in the positive electrode mixture layer or the negative electrode mixture layer 12 include carbon black such as Acetylene Black (AB) or Ketjen Black (KB), carbon materials such as graphite powder, and conductive metal powder such as nickel powder. One of these may be used, or two or more of them may be used in combination.
[ Binders ]
Examples of the binder used in the positive electrode material mixture layer or the negative electrode material mixture layer 12 include cellulose polymers, fluorine resins, vinyl acetate copolymers, and rubbers. Specifically, examples of the binder in the case of using a solvent-based dispersion medium include polyvinylidene fluoride (PVDF), Polyimide (PI), polyvinylidene chloride (PVDC), and polyethylene oxide (PEO), and examples of the binder in the case of using an aqueous dispersion medium include styrene-butadiene rubber (SBR), acrylic-modified SBR resin (SBR-based latex), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), Polytetrafluoroethylene (PTFE), hydroxypropyl methyl cellulose (HPMC), and tetrafluoroethylene-hexafluoropropylene copolymer (FEP). One of these may be used, or two or more of them may be used in combination.
(organic Artificial SEI layer)
As shown in fig. 1, the negative electrode 1 of the present embodiment has an organic artificial SEI layer 14 formed so as to cover the surface of the negative electrode mixture layer 12. The organic artificial SEI layer 14 is configured to have multi-branched molecules 13, and the multi-branched molecules 13 are bonded to the particle surfaces of the negative electrode active material 11 constituting the negative electrode mixture layer 12. By covering the surface of the negative electrode mixture layer 12 with the multi-branched molecules 13, lithium ions can be transferred between the negative electrode active material 11 and the electrolytic solution, and the electrolytic solution molecules 3 can be prevented from reaching the negative electrode mixture layer 12, so that decomposition of the electrolytic solution can be suppressed and the durability can be improved. In addition, since the formation or composition of SEI on the surface of the negative electrode can be controlled, the output and charging performance of the lithium ion secondary battery can be improved. The interface formed between the multi-branched molecules 13 and the electrolyte according to the present embodiment can suppress a side reaction during the lithium ion reduction reaction, and can stably perform the lithium reduction reaction on the negative electrode 1. The negative electrode 1 of the present embodiment is effective in a reaction of reducing lithium ions, and can be applied to a lithium ion secondary battery, a lithium metal battery, and the like. The multi-branched molecules 13 may be bonded to the surface of the conductive aid or the surface of the current collector, for example, and can also suppress side reactions during the reduction reaction of lithium ions.
[ Multi-branched molecule ]
The multi-branched molecule 13 is preferably composed of a dendrimer, for example. Examples of the dendrimer include a dendron, a dendrimer, and a hyperbranched polymer.
The number average molecular weight of the multi-branched molecule 13 is preferably 300 to 100000, and more preferably 800 to 10000. If the number average molecular weight is within the above range, the lithium intercalation surface on the surface of the negative electrode active material particle can be sufficiently covered, and direct contact between the electrolyte and the lithium intercalation surface is suppressed, so that the durability of the electrode and the electrolyte can be improved. The multi-branched molecules 13 cover the negative electrode mixture layer 12 to such an extent that lithium migration is not inhibited, and exhibit good lithium ion conductivity.
The multi-branched molecule 13 preferably has 4 or more molecular terminal portions in one molecule. When the multi-branched molecules 13 have the number of molecular terminal portions within the above range, if the molecular terminal portions have the specific functional groups, the probability of contact between the adsorbing groups (specific functional groups) and the negative electrode mixture layer 12 increases, the adsorbing amount is within an appropriate range, and the molecules can be strongly adsorbed and bonded, thereby covering the surface of the negative electrode mixture layer 12. The multi-branched molecule 13 preferably has 4 or more and 64 or less molecular terminal portions, and more preferably 8 or more hydroxyl groups and at least one carboxyl group.
The negative electrode mixture layer 12 preferably has hydroxyl groups or carboxyl groups on the surface. This allows condensation with the multi-branched molecules 13 having hydroxyl or carboxyl groups, thereby forming the organic artificial SEI layer 14 on the surface.
The dendrons useful in the present invention can be synthesized by a usual method, and commercially available products can be used. Such commercial products are available, for example, from Aldrich. Specific examples of the dendron produced by Aldrich include polyester-8-hydroxy-1-acetylene bis-MPA dendrimer, 3 rd generation (catalog No. 686646); polyester-16-hydroxy-1-acetylene bis-MPA dendrimer, generation 4 (Cat: 686638); polyester-32-hydroxy-1-acetylene bis-MPA dendrimer, generation 5 (catalog No. 686611); polyester-8-hydroxy-1-carboxy bis-MPA dendrimer, generation 3 (catalog No. 686670); polyester-16-hydroxy-1-carboxy bis-MPA dendrimer, generation 4 (Cat: 686662); and polyester-32-hydroxy-1-carboxy bis-MPA dendrimer, generation 5 (catalog No.: 686654).
The dendritic polymer usable in the present invention can be synthesized by a usual method, and can be purchased as a commercial product from Aldrich. Examples thereof include amino group-terminated polyamidoamine dendrimers, ethylenediamine cores, 0.0 generation (catalog No. 412368); polyamidoamine dendrimers, ethylenediamine cores, generation 1.0 (cat # 412368); polyamidoamine dendrimers, ethylenediamine cores, generation 2.0 (cat # 412406); polyamidoamine dendrimers, ethylenediamine cores, generation 3.0 (cat # 412422); polyamidoamine dendrimers, ethylenediamine cores, generation 4.0 (cat # 412446); polyamidoamine dendrimers, ethylenediamine cores, generation 5.0 (cat # 536709); polyamidoamine dendrimers, ethylenediamine cores, generation 6.0 (cat # 536717); polyamidoamine dendrimers, ethylenediamine cores, generation 7.0 (cat # 536725), and the like. In addition to the amino group at the end, dendritic polymers having a hydroxyl group, a carboxyl group, or a trialkoxysilyl group at the end can also be purchased.
The hyperbranched polymer that can be used in the present invention can be synthesized by a usual method, and can be purchased from Aldrich company as a commercial product. For example, hyperbranched bis-MPA polyester-16-hydroxy, generation 2 (cat # 686603); hyperbranched bis-MPA polyester-32-hydroxy, generation 3 (catalog number: 686581); hyperbranched BIS-MPA polyester-64-hydroxy, 4 th generation (catalog number: 686573), and the like. Any reaction can also be used to impart substituents to these terminal reactive groups.
The filling ratio of the negative electrode active material 11 in the negative electrode is preferably 65% or more. Thus, a lithium ion battery having an improved energy density of the electrode and a high output or a small size can be manufactured. Conventionally, if the filling ratio of the negative electrode active material particles 11 is increased, the following problems occur: electrolyte molecules 3 penetrating between the particles of negative electrode active material 11 are decomposed inside negative electrode mixture layer 12 to form SEI, which increases interface resistance. In the lithium ion battery 100 of the present embodiment, the organic artificial SEI layer 14 can prevent the electrolyte molecules 3 from entering between the particles of the negative electrode active material 11, and can prevent an increase in interface resistance.
(Current collectors)
As the material of the positive electrode current collector and the negative electrode current collector, a foil or plate, a carbon sheet, a carbon nanotube sheet, or the like of copper, aluminum, nickel, titanium, stainless steel can be used. The above materials may be used alone, or a metal-clad foil composed of two or more kinds of materials may be used as necessary. The thickness of the positive electrode current collector and the negative electrode current collector is not particularly limited, and may be, for example, in the range of 5 to 100 μm. The thickness of the positive electrode current collector 2 and the negative electrode current collector 5 is preferably in the range of 7 to 20 μm from the viewpoint of structure and improvement of performance.
(diaphragm)
The separator is not particularly limited, and examples thereof include a porous resin sheet (film, nonwoven fabric, etc.) made of a resin such as Polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide.
(electrolyte)
As the electrolytic solution, an electrolytic solution composed of a nonaqueous solvent and an electrolyte can be used. The concentration of the electrolyte is preferably in the range of 0.1 to 10 mol/L.
An additive containing at least one compound selected from the group consisting of vinylene carbonate, fluoroethylene carbonate and propane sultone may be added to the electrolyte.
Thus, by using an electrolytic solution to which a compound having reductive decomposition properties and being easy to form an SEI film is added, the added compound is decomposed in preference to the electrolytic solution to form an SEI film on the negative electrode, and therefore, the durability of the electrolytic solution is further improved. When used in combination with the negative electrode having the organic artificial SEI layer 14 formed by the multi-branched molecules 13, the SEI can be stabilized, and the types of additives and the resistance of the electrolyte can be reduced.
[ non-aqueous solvent ]
The nonaqueous solvent contained in the electrolyte solution is not particularly limited, and examples thereof include aprotic solvents such as carbonates, esters, ethers, nitriles, sulfones, and lactones. Specific examples thereof include Ethylene Carbonate (EC), Propylene Carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), Ethyl Methyl Carbonate (EMC), 1, 2-Dimethoxyethane (DME), 1, 2-Diethoxyethane (DEE), Tetrahydrofuran (THF), 2-methyltetrahydrofuran, dioxane, 1, 3-dioxolane, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, Acetonitrile (AN), propionitrile, nitromethane, N-Dimethylformamide (DMF), dimethyl sulfoxide, sulfolane and γ -butyrolactone.
[ electrolyte ]
Examples of the electrolyte contained in the electrolytic solution include LiPF6、LiBF4、LiClO4、LiN(SO2CF3)、LiN(SO2C2F5)2、LiCF3SO3、LiC4F9SO3、LiC(SO2CF3)3、LiF、LiCl、LiI、Li2S、Li3N、Li3P、Li10GeP2S12(LGPS)、Li3PS4、Li6PS5Cl、Li7P2S8I、LixPOyNz(x＝2y+3z－5，LiPON)、Li7La3Zr2O12(LLZO)、Li3xLa2/3-xTiO3(LLTO)、Li1+xAlxTi2-x(PO4)3(0≦x≦1，LATP)、Li1.5Al0.5Ge1.5(PO4)3(LAGP)、Li1+x+yAlxTi2-xSiyP3-yO12、Li1+x+yAlx(Ti,Ge)2-xSiyP3-yO12、Li4-2xZnxGeO4(LISICON) and the like. Among them, LiPF is preferably used6、LiBF4Or mixtures thereof as the electrolyte.
Examples of the electrolyte solution include an ionic liquid, and an electrolyte solution containing a polymer containing an aliphatic chain such as polyethylene oxide (PEO) or a polyvinylidene fluoride (PVDF) copolymer in the ionic liquid. The electrolyte solution containing an ionic liquid can flexibly cover the surface of the positive electrode active material or the negative electrode active material, and can form a site that undergoes ion transfer by contacting the surface of the positive electrode active material or the negative electrode active material 11.
The present invention is not limited to the above-described embodiments, and variations and modifications within a range that can achieve the object of the present invention are included in the present invention. For example, a nonaqueous electrolyte secondary battery is a secondary battery (power storage device) using a nonaqueous electrolyte such as an organic solvent as an electrolyte, and includes a sodium ion secondary battery, a potassium ion secondary battery, a magnesium ion secondary battery, a calcium ion secondary battery, and the like in addition to a lithium ion secondary battery. The lithium ion secondary battery is a nonaqueous electrolyte secondary battery not containing water as a main component, and refers to a battery containing lithium ions in a carrier responsible for electric conduction. Examples of the lithium ion secondary battery include a lithium metal ion battery, a lithium polymer battery, an all solid lithium battery, and an air lithium ion battery. The same applies to other secondary batteries. Here, the nonaqueous electrolyte not containing water as a main component means that the main component in the electrolyte is not water. That is, it is a known electrolyte used in a nonaqueous electrolyte secondary battery. This electrolyte can be used as a secondary battery even when it contains a small amount of water, but it is preferable to contain as little water as possible because it adversely affects the cycle characteristics, storage characteristics, and input/output characteristics of the secondary battery. In practice, the amount of water in the electrolyte is preferably 5000ppm or less.
[ examples ]
The present invention will be described in more detail below with reference to examples. The contents of the present invention are not limited to the description of the following examples.
The positive and negative electrodes of examples 1 to 10 and comparative example 1 were produced. The composition of the negative electrode and the composition of the positive electrode in each example are shown in table 1 and table 3, respectively. Further, the details of the kinds of the multi-branched molecules shown in Table 1 are shown in Table 2. Further, the compositions of the electrolytes shown in table 1 are shown in table 4.
(preparation of Positive electrode)
Mixing a conductive auxiliary agent with polyvinylidene fluoride (PVDF), dispersing by using a rotation revolution stirrer, and mixing Li1Ni0.6Co0.2Mn0.2O2(NCM622) As a positive electrode active material, mixing was carried out using a planetary mixer. Then, N-methyl-N-pyrrolidone (NMP) was added to prepare an electrode paste. This electrode paste was applied to an Al collector, dried, and then pressed by a roll press, and dried in a vacuum at 120 ℃. The electrode plate thus produced was punched out to a size of 30mm × 40 mm. The thickness of the positive electrode plate was 70 μm.
(preparation of cathode)
Carboxymethyl cellulose (CMC) was mixed with a conductive aid, and dispersed using a planetary mixer. Then, the negative electrode materials of the following examples were mixed and dispersed again using a planetary mixer. Then, a dispersion solvent and SBR were added to the mixture to disperse the mixture, thereby preparing an electrode paste. This electrode paste was applied to a Cu collector, dried, and then pressed by a roll press, and dried in a vacuum at 100 ℃. The electrode plate thus produced was punched into 34mm × 44 mm. The thickness of the negative electrode plate was 90 μm.
(preparation of negative electrode Material)
In order to produce the negative electrode material of example 1, 96.3 parts by weight of graphite and 0.2 part by weight of the multi-branched molecular compound No.1 shown in Table 2 were weighed and stirred in an aqueous solution for 1 hour. Then, the resultant was dried under reduced pressure at 150 ℃ for 12 hours to obtain a negative electrode material in which organic molecules were bonded to the surface of the active material.
In the production of the negative electrode materials of examples 2 to 10, the graphite and the multi-branched molecular compound in the weight parts shown in table 1 were measured in the same manner as in example 1, and stirred in an aqueous solution for 1 hour. Then, the resultant was dried under reduced pressure at 150 ℃ for 12 hours to obtain a negative electrode material in which organic molecules were bonded to the surface of the active material.
The negative electrode material of comparative example 1 used untreated graphite.
(production of lithium ion Secondary Battery)
A lithium ion secondary battery was fabricated by introducing a laminate in which a separator was interposed between the positive electrode and the negative electrode fabricated above into a container in which an aluminum laminate for a secondary battery (manufactured by Dai Nippon Printing co., Ltd.) was heat-sealed and processed into a bag shape, and injecting an electrolyte into the interface of each electrode.
< evaluation >
The following evaluations were performed on lithium ion secondary batteries manufactured using the electrodes of examples 1 to 10 and comparative example 1.
[ initial Capacity ]
Under the condition of 25 ℃, the battery is charged to 4.2V at 0.2C, and then discharged to 2.5V at 0.2C. The discharge capacity at the 5 th discharge was defined as the initial capacity by repeating the above 5 times.
[ initial internal resistance value of Battery ]
The lithium ion secondary battery after the initial capacity measurement was left at the measurement temperature (25 ℃) for 1 hour, and then charged at 0.2C, and the charge amount (soc (state of charge)) was adjusted to 50%, and left for 10 minutes. Then, the C rate was set to 0.5C, pulse discharge was performed for 10 seconds, and the voltage at 10 seconds of discharge was measured. Then, the horizontal axis represents a current value, the vertical axis represents a voltage, and the voltage at 10 seconds of discharge corresponding to the current at 0.5C is plotted. After leaving for 10 minutes, the SOC was recovered to 50% by auxiliary charging, and then left for another 10 minutes. The above operation was performed for each C rate of 1.0C, 1.5C, 2.0C, 2.5C, and 3.0C, and the voltage at 10 seconds of discharge corresponding to the current value at each C rate was plotted. The slope of the approximate line obtained by the least square method obtained from each graph was used as the internal resistance value (Ω) of the lithium ion secondary battery obtained in this example. The results are shown in Table 1.
[ discharge capacity after storage durability ]
The lithium ion secondary battery after the initial internal resistance value measurement was charged to 4.2V at 0.2C and stored at 45 ℃ for 84 days to perform a storage durability test. After storage, the cells were discharged at 25 ℃ to 2.5V at 0.2C, charged again to 4.2V at 0.2C, and discharged to 2.5V at 0.2C. The results are shown in Table 1. The current value at which discharge was completed within 1 hour for the obtained discharge capacity was set to 1C.
[ internal resistance value of Battery after storage durability ]
The lithium ion secondary battery after the discharge capacity after the storage endurance was measured was charged to (soc of charge) 50% in the same manner as the measurement of the initial battery internal resistance value, and the battery internal resistance value (Ω) after the storage endurance was determined by the same method as the measurement of the initial battery internal resistance value. The results are shown in Table 1.
[ Capacity conservation Rate after storage durability ]
The ratio of the discharge capacity (mAh) after the storage durability to the initial discharge capacity (mAh) was determined as the capacity retention rate (%) after the storage durability. The results are shown in Table 1.
[ increase in resistance after storage durability ]
The ratio of the internal resistance value (Ω) of the battery after the storage durability to the initial internal resistance value (Ω) of the battery was obtained as the resistance increase rate (%) after the storage durability. The results are shown in Table 1.
[ analysis of the surface of the negative electrode of the battery after storage durability ]
For example 3 and comparative example 1, the batteries after storage endurance were discharged to 2.5V at 0.2C. The battery was disassembled and the negative electrode was taken out, washed in DMC solvent and dried. Then, the electron state of the surface of the negative electrode was analyzed by X-ray photoelectron spectroscopy (hereinafter referred to as "XPS"). In the XPS measurement, the atomic composition percentage (atom%) of the element attached to the surface of the negative electrode was measured. The thickness of the coating film is determined by converting SiO2The depth was determined and defined as the depth at which oxygen was halved. The results are shown in Table 5. It is found that the thickness of the SEI decreases by the bonding of the molecules, and the composition of the SEI or the inorganic components changes. Example 3 and comparative example 1The relationship between the depth and the composition in (1) is shown in fig. 2 and 3.
[ Table 1]
[ Table 2]
[ Table 3]
[ Table 4]
| Electrolyte solution | Composition of |
| A | 1.2M LiPF6+EC/EMC/DMC(3/3/4)+PS 1％+VC 1％ |
| B | 1.0M LiPF6+0.2M LiFSI EC/EMC/DMC(3/3/4)+PS 1％+VC 1％ |
[ Table 5]
| Film thickness (nm) | |
| Example 3 | 130 |
| Comparative example 1 | 160 |
From the results of table 1, the following results were confirmed: the lithium ion secondary batteries in the respective examples had higher capacity retention rate after endurance and lower resistance increase rate after endurance, as compared with the lithium ion secondary batteries in the comparative examples. That is, it was confirmed that the lithium ion secondary batteries of the respective examples have excellent durability by having a multi-branched molecule including any one of a dendron, a dendrimer and a hyperbranched polymer on both surfaces of the particles of the negative electrode active material.
Reference numerals
100 lithium ion secondary battery
1 negative electrode
11 negative electrode active material
12 negative electrode mixture layer
13 Multi-branched molecule
14 organic artificial SEI layer
2 lithium ion
3 electrolyte molecules.
Claims (7)
1. A negative electrode for a nonaqueous electrolyte secondary battery, which has a multi-branched molecule bonded to the surface of a negative electrode material comprising a negative electrode active material, a conductive assistant and a current collector.
2. The negative electrode for a nonaqueous electrolyte secondary battery according to claim 1, wherein the multi-branched molecule is composed of at least one compound selected from the group consisting of a dendron, a dendrimer and a hyperbranched polymer.
3. The negative electrode for a nonaqueous electrolyte secondary battery according to claim 1, wherein the multi-branched molecule has a number average molecular weight of 300 or more and has 4 or more molecular terminal portions in one molecule.
4. The negative electrode for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the negative electrode active material has a functional group on a surface thereof,
the multi-branched molecule is bonded to the functional group.
5. The negative electrode for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein a filling rate of the negative electrode active material in the negative electrode is 65% or more.
6. A nonaqueous electrolyte secondary battery comprising the negative electrode for nonaqueous electrolyte secondary batteries according to any one of claims 1 to 3.
7. The nonaqueous electrolyte secondary battery according to claim 6, wherein at least one compound selected from the group consisting of vinylene carbonate, fluoroethylene carbonate and propane sultone is further added to the electrolyte.
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| JP2020-168270 | 2020-10-05 | ||
| JP2020168270A JP2022060673A (en) | 2020-10-05 | 2020-10-05 | Negative electrode for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery comprising the same |
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| US (1) | US20220109144A1 (en) |
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| US20220109144A1 (en) | 2022-04-07 |
| JP2022060673A (en) | 2022-04-15 |
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